Are you getting a RPM surge at idle? You can test the EGR with a hand held vacuum pump. First see if it holds vacuum. You can remove it and clean it. You can unplug the vacuum line and see how it runs. You can remove it and see if the plunger even moves or if its siezed up. See if will hold a vacuum first. Cant hurt to spray some carb cleaner around all your vacuum lines while its running to see if you may have a vacuum leak anywhere. Start there and work your way to removing and cleaning the EGR valve. Not a bad job on a small block chevy. Let me know what you find.